I agree with the age thing....to a point. But there is also the factor of 'natural ablility' (talent), and many other things from hand size to spousal support.
Personally i am convinced that age might be a lesser factor (except for the top end)
There is also dedication (maybe the most important part of learning and improving any skill.
And then there is the training method/teacher, to whome you need a connection of some sort, its important that both you and the teacher/method have the same goals.
i am a firm beleiver that if your basic training is piano, and the methose teaches you all basics like playing from sheet music, musical theory, playing by ear, improvising and gradually improves all of these... that its easier to addapt from piano to otehr keyboard instruments, then the other way around.
There is another thing to remember, where learning bass takes like 6 months and guitar about 2 to 3 years... getting a professional level on any keyboard and espescially piano might take up to a decade..